[nix] Add detsys installer

Author: mikeland73

internal/boxcli/featureflag/detsys.go

@@ -0,0 +1,3 @@
+package featureflag
+
+var UseDetSysInstaller = cicdOnly("DETSYS_INSTALLER")

internal/boxcli/featureflag/feature.go

@@ -43,6 +43,13 @@ func enable(name string) *feature {
 	return features[name]
 }
 
+func cicdOnly(name string) *feature {
+	if os.Getenv("CI") != "" || os.Getenv("CIRCLECI") != "" || os.Getenv("GITHUB_ACTIONS") != "" {
+		enable(name)
+	}
+	return disable(name)
+}
+
 var logMap = map[string]bool{}
 
 func (f *feature) Enabled() bool {

internal/boxcli/setup.go

@@ -29,13 +29,19 @@ func setupCmd() *cobra.Command {
 		},
 	}
 
-	installNixCommand.Flags().Bool(nixDaemonFlag, false, "Install Nix in multi-user mode.")
+	installNixCommand.Flags().Bool(
+		nixDaemonFlag,
+		false,
+		"Install Nix in multi-user mode. This flag is not supported if you are using DetSys installer",
+	)
 	setupCommand.AddCommand(installNixCommand)
 	return setupCommand
 }
 
 func runInstallNixCmd(cmd *cobra.Command) error {
 	if nix.BinaryInstalled() {
+		// TODO: If existing installation is not detsys, but new installation is detsys can we detect
+		// that and replace it?
 		ux.Finfof(
 			cmd.ErrOrStderr(),
 			"Nix is already installed. If this is incorrect "+

internal/nix/install.go

@@ -16,6 +16,7 @@ import (
 	"github.com/mattn/go-isatty"
 	"github.com/pkg/errors"
 
+	"go.jetpack.io/devbox/internal/boxcli/featureflag"
 	"go.jetpack.io/devbox/internal/boxcli/usererr"
 	"go.jetpack.io/devbox/internal/build"
 	"go.jetpack.io/devbox/internal/cmdutil"
@@ -39,11 +40,20 @@ func Install(writer io.Writer, daemon *bool) error {
 	defer r.Close()
 
 	installScript := "curl -L https://releases.nixos.org/nix/nix-2.18.1/install | sh -s"
-	if daemon != nil {
-		if *daemon {
-			installScript += " -- --daemon"
-		} else {
-			installScript += " -- --no-daemon"
+	if featureflag.UseDetSysInstaller.Enabled() {
+		// Should we pin version? Or just trust detsys
+		installScript = "curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install"
+		if isLinuxWithoutSystemd() {
+			installScript += " linux --init none"
+		}
+		installScript += " --no-confirm"
+	} else {
+		if daemon != nil {
+			if *daemon {
+				installScript += " -- --daemon"
+			} else {
+				installScript += " -- --no-daemon"
+			}
 		}
 	}
 
@@ -169,3 +179,14 @@ func EnsureNixInstalled(writer io.Writer, withDaemonFunc func() *bool) (err erro
 	fmt.Fprintln(writer, "Nix installed successfully. Devbox is ready to use!")
 	return nil
 }
+
+func isLinuxWithoutSystemd() bool {
+	if build.OS() != build.OSLinux {
+		return false
+	}
+	// My best interpretation of https://github.com/DeterminateSystems/nix-installer/blob/66ad2759a3ecb6da345373e3c413c25303305e25/src/action/common/configure_init_service.rs#L108-L118
+	if _, err := os.Stat("/run/systemd/system"); errors.Is(err, os.ErrNotExist) {
+		return true
+	}
+	return !cmdutil.Exists("systemctl")
+}